In a known apparatus, U.S. Pat. No. 3,981,671, the mold holder support is constructed in a C-shape. Of the two clamping plates for the parts of the mold that are located one above the other on this C-shaped support, the upper one is placed directly on the upper leg of the support. The lower plate is supported in such a way that it can move up and down, by the lower leg of the support. A base plate is interposed with lift cylinders, and guide rods are provided for the movement of the lower clamping plate back and forth toward the upper clamping plate. The result of this type of support for the lower plate is that it, and consequently the part of the mold on it, are in a comparatively high location in the lowest position, and furthermore, the lower part of the mold always has to be moved up to a high position over a large distance that actually is not necessary when medium-sized and small, or large, flat shaped bodies are being produced. This is because the upper plate is located at a distance from the lower plate which makes it possible also to fasten the parts of molds for the production of larger shaped bodies to the plates. Furthermore, each of the plates can be revolved, by means of working cylinders, around one of the parallel axes corresponding to them by about 45.degree. out of its parallel position to the other fixing plate, so that both plates are opened up approximately like books after the revolving has taken place. The revolving of the mold holder around an axis that is located parallel to the previously-mentioned parallel axes of its clamping plates is produced by working cylinders which are pivoted on the support for the apparatus, on the one hand, and on the C-shaped support of the mold holder, on the other.
In this known apparatus, it is disadvantageous that, as a result of the high location of the lower clamping plate in the basic position, servicing the apparatus is comparatively difficult--for example, when removing foamed shaped pieces from the lower part of the mold and when cleaning and preparing that part of the mold for the next foaming process, and, furthermore, a relatively large amount of time is required for opening and closing the mold when producing medium-sized and small, as well as large, flat shaped bodies. Also the C-shaped construction of the mold holder support is disadvantageous. Because of this construction the mold is accessible from three sides when it is closed, but not in the middle of the fourth side or in the middle from above and below. This has an especially negative effect when making use of an under surface foaming process wherein the materials are injected into the mold from its bottom or underside since it does not permit making use of it under any circumstances.
Another disadvantage of that apparatus is the fact that the forces coming into being during the foaming process go into the C-shaped support of the mold holder, but qualified by the fact that, ultimately, both clamping plates are supported by the jaws of the support. Because of this situation, the maximum foaming pressure must be taken into consideration when designing both the two clamping plates and the C-shaped support if no distortion of the foaming pressure is to take place.
Thus, especially because of its construction, the known apparatus is not particularly easy to service in the first place, has mechanical idle periods that are too long when producing medium-sized and small parts and large, flat pieces in the second place, and, finally, it has an unfavorable force distribution during the foaming process.